Electron discharge tube having a secondary emissive electrode



Dec. 23, 1952 G. DIEMER ELECTRON DISCHARGE TUBE HAVING A SECONDARY EMISSIVE ELECTRODE 2 SHEETSSHEET 1 Filed Dec. 20, 1947 ZZZ 2. 22 9 m? H WBWM w w E J Mk Dec. 23, 1952 G. DIEMER ELECTRON DISCHARGE TUBE HAVING A SECONDARY EMISSIVE ELECTRODE 2 SHEETS-SHEET 2 Filed Dec. 20, 1947 INVENTOR. GESflVI/S DIBMER %z%% AGEZVI Patented Dec. 23, 1952 UNITED STATES OFFICE ELECTRON DISCHARGE TUBE HAVING Ay SECONDARY 'EMISSI-VE ELECTRODE ApplicationDecember 20, 1947, Serial No.- 793,038

In the Netherlands January 8, 1947.

4 Claims. 1.: Thea-inventionrelatesto. a. devicelfor, transmitting or-producing; electrical oscillations having a wavelengthofi theorder-of magnitude of somefew decimetres bygmeans of an electricdischar g.tube

comprising; at leastone cathode, oneanode-and a secondary-emission. electrode in theisaid order. Theinventio-n also relates to a discharge tube for use in such a: device.

It. is already known to produce'short waves by means-of secondary-emission tubes in a so-called tetrode arrangement; in which, viewed from the cathode, the'wiresof the-.control-grid and the perforated anode provided to constitute agricl wound on edge are located in succession and in which the plate-shaped secondary-emission electrode surroundsthe assembly. The results thus obtained arehighlysatisfactory in the wavelength range from Sto. 1,, by' reason of the small divergence in, the transit times of the primary and the secondary electrons. With shorter waves, however, theresultsiare rapidly impaired, since shadow grids of, the. required small dimensions can be realized with difiiculty only and in'addition part of-the primary electrons is always directly intercepted by the anode.

Itis also known to produce short waves with the aid of a cavity resonatorv tube, in which the elongated cathode. faces aslit in an elongated resonant, cavity, the edges of which form the anode, whilst the rear wall of the resonant cavity is secondarily emitting and in which, on account orgthediiferent voltages. across anode and secondary-emission. electrode. the: face. and the rear of the resonant cavity are not coupled galvanically, but only capacitatively. The primary electrons are bunched bya magnetic field extending in their direction of movement. Al'- though this involves a slightv transit time divergenceior the. primary electrons, the effect-of th'egmagnetic field is comparatively unfavourable in that. itprevents, thesecondary electrons from being rapidly intercepted by: the anode andthus results. in undue. space, charge and transit time divergence.

The said disadvantages can be largely obviated by using a device according to the invention.

According to the invention, in a device for transmitting or producing electrical oscillations having a wavelength of the order of magnitude of some few decimetres by means of an electric discharge tube comprising at least one cathode, one perforated anode and one secondary-emission electrode in the said order, the electrons, after leaving the cathode. are bunched electrostatically so as to pass through an aperture in the anode,

and. t e; su stantially lat se is n dewliichis at rightangles to the direction thecathode, exhibits asmallsalient part which is directed towards the cathode and which, according asz the system, has a symmetry plane oraxis, terminates in a-sharp ledge or tip, whilst the; primary electrons, are projected on to the salient part and the area directly. adjacent it.

The, primary electrons directed towards the centre of thesecondary-emission electrode find theinway1 to the sides of the salient part, where the electrical field is very; favourably directed for the interception; of the secondary electrons by the anode-in contradistinction; to the field that may be, developed in the, caseof completely fl-at secondary emisslonelectrodes. Secondary electrons arethus prevented from returning to the. cathodeanode space and hence from being given an excessive transit time.- The salient part may protrude to the extent of extending bewteen the parts of the, anode, this extent, however, not exceeding half the thickness. Only if this condition iszfulfilled, the concentration of the primary electrons on the. secondary-emission electrode does not vary. with the voltage across the latter and, even in the case of extensive control of the secondary-emission electrode the secondary electrons are effectively, intercepted. Accordingly these tubes. permit. of working with a voltage across the; secondary-emission electrode which is only a fraction of the; anode voltage; itis true that in this casethe oscillations produced are greatly distorted, but this is not inconvenient in the; caseof. uplin o a ie a tc v ty.

Inorderr hatth inv ntionamev bem r l t understoodand. ea y, a ed into f it will now; be; described with reference to the accompanying, drawing in which Fig. 1 is a horion al-.-seetional-viewoi e e c. di c a e tub ccor ng; tothe. n ent on. hic com s a control-grid, Fig. 2 is a vertical sectional view of an electric discharge tube according to the invention. n wh-iQhl ev anode. and he. secon emission electrode are directly sealed in the wall; Fig. 3 is a view, in cross-section, along line 33 of Fig. 2, and Fig. 4 is a view, in cross-section, along line 44 of Fig. 2.

Referring to Fig. l, l designates a flat cathode which is adapted to emit on two sides. Bridge supporting rods 2 have wound on them the wires 3 of the control-grid, and at the outside of the grid, on either side of the cathode, there are arranged two rods 4 lying in a plane by which the electrons emanating from the cathode are bunched so as to impinge not on the anode constituted by rods 5, but on the secondary-emission electrode 6 arranged on either side of the cathode, this impingement occurring substantially on the flanks of the protruding ledge 1 and the area directly adjacent it. By reason of the shape of the secondary-emission electrode as shown and the arrangement of the anode the secondary electrons are sucked away by a field which is substantially at right angles to the direction of movement of the primary electrons. Since the tube comprises a control-grid it is adapted to be used not only as a valve oscillator but also as an amplifier. The spacings betweenthe electrodes may be derived from the adjoining scale and the length of the system is approximately 5 mms. At a wavelength of 50 cms. a gain in energy of 70 may be attained at a bandwidth of 2 mc./s.

Referring to Fig. 2, l designates the glass wall of the discharge tube, the bottom H of which has sealed in it three solid studs for the filament supply and the cathode lead. In front of the fiat cathode 13, which emits upwards there-is arranged a partly conical bunching screen l5 (the tube exhibits cylinder symmetry) which, together with the cathode, is secured to a mica screen I4. This screen is secured, by means of two glass beads E5 to a planar anode ii. The anode carries a conical screen 58, which projects the bunched primary electrons through an aperture E9 in the anode to the salient tip 2 l of the secondary-emission electrode 20. The anode and the secondary-emission electrode are sealed, in the form of flat discs, directly into or onto the glass wall (so-called disc seal) the distance between the flat part of the anode and the secondary-emission electrode is approximately 0.5 mm. On connection of the tube by means of theprotruding edges of anode and secondary-emission electrode to a tunable cavity resonator suitable for this purpose, the tube is adapted to oscillate at a wavelength of from 40 to 10 cms. At an anode voltage of 1200 volts and a voltage across the secondary-emission electrode of 100 volts, the current of the secondary-emission electrode is 10 milli-amperes (the secondary-emission electrode has been treated with caesium oxide). The output is at a wavelength of cms. and 10% at a wavelength of 15 cms. Sealed in addition on top of the secondary-emission electrode is a glass wall 22 which permits of cooling the secondary-emission electrode in a simple man" ner with a sufficient supply of water.

WhatI claim is:

1. An electron discharge tube comprising a cathode source of electrons, means to form said electrons into a beam, a planar anode having the plane thereof arranged substantially perpendicular to said beam and being provided with an aperture through which said beam passes, and a secondary emissive electrode positioned on the side of said anode remote from said cathode source, said secondary emissive electrode having a salient portion thereof arranged in the path of said beam and positioned closer to the plane of said anode than the remaining effective portion of said secondary emissive electrode.

2. An electron discharge tube comprising a cathode source of electrons, means to form said electrons into a beam, a planar anode havingthe plane thereof arranged substantially perpendicular to said beam and being provided with an aperture through which the said beam passes, and a secondary emissive electrode positioned on the side of said anode remote from said cathode source, said secondary emissive electrode having a salient portion thereof arranged in the path of said beam and extending into said aperture whereby said salient portion is positioned closer to the plane of said anode than the remaining effective portion of said secondary emissive electrode.

3. An electron discharge tube comprising a cathode source of electrons, means to form said electrons into a beam,-an anode comprising two rod-shaped members spaced apart and arranged in a plane substantially perpendicularv tosaid beam, said spaced rod-shaped members defining an aperture through which said beam passes, a control grid interposed between said cathode and said anode, and a secondary emissive electrode positioned on the side of said anode remote from said cathode source, said secondary emissive electrode having a salient portion thereof arranged in the path of said beam and positioned closer to the plane of said anode than the remaining effective portion of said secondary emissive electrode.

4. An electron discharge tube comprising a cathode source of electrons, means to form said electrons into a beam, a disc shaped planar anode having the plane thereof arranged substantially perpendicular to said beam and being provided with a central aperture through which said beam passes, and a disc shaped secondary emissive electrode positioned on the side of said anode remote from said cathode source, said secondary emissive electrode having a central cup-shaped portion extending towards said anode and a salient portion of said cup-shaped portion arranged in the path of said beam and positioned closer to the plane of said anode than the remaining portions of said cup-shaped portion.

GESINUS DIEMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,104,100 Roberts Jan. 4, 1938 2,218,744 Colberg Oct. 22, 1940 2,266,639 Hollmann Dec. '16, 1941 2,357,922 Ziebolz et a1 Sept. 12, 1944 2,372,450 Rajchman et a1. Mar. 27, 1945 2,416,302 Goodall Feb. 25, 1947 

